The present invention relates to a device for cooling of a heat-generating member which is placed in a liquid located in a pressure vessel, which liquid is adapted to serve as a coolant for the heat-generating member. The present invention is specially directed to the case where the heat-generating member consists of a core in a nuclear reactor of the type in which the reactor vessel is arranged in a neutron-absorbing liquid, for example an aqueous solution of boric acid, and the reactor coolant in the lower and upper ends of the reactor is arranged in hydraulic communication with the neutron-absorbing liquid. During normal operation the core in such a reactor is cooled by means of a coolant flow, normally a light water flow, continuously flowing through the core and the reactor vessel, the heat contents of the flow being utilized in a steam generator, or other heat exchanger, before the coolant is returned to the reactor vessel for repeated heating in the core. A reactor of such a kind is described, inter alia, in Swedish patent specifications Nos. 7606622-4 and 8102000-0.
In case of an operational disturbance, an established pressure equilibrium between the neutron-absorbing liquid and the reactor coolant is disrupted, resulting in the neutron-absorbing liquid flowing into the reactor core and in the rest of the reactor, so that the power thereof is reduced to the decay power. The core with its "inherent" heat generation is then situated in the neutron-absorbing liquid.
Operating situations with decay power cooling of the reactor core may occur both with a pressurized pressure vessel and with the vessel pressure-relieved to a pressure which only somewhat exceeds the atmospheric pressure. In certain hypothetical cases the pressure may be almost as great outside the pressure vessel as inside the same. The reason for the pressure relief may be rupture on the pressure vessel or on a pressurized tube connected to the pressure vessel. Operating situations with decay power cooling of the reactor core may also occur, inter alia, in the event of interruption in the supply of electric power or in case of disturbance in the supply of coolant to the reactor core. In the case of decay power cooling of the core, the heat can be removed passively from the core with the aid of a medium flow which may consist of a liquid or steam or a combination thereof.
The present invention makes it possible to ensure an efficient cooling of the liquid in the pressure vessel in nearly all operating situations with decay power cooling.
The favourable result obtained according to the invention can primarily be attributed to the fact that the cooling of the liquid in the pressure vessel takes place under self-circulation of a flow of liquid and/or of steam of the liquid with any contents of uncondensable gas in a circulation system containing an evaporator arranged in an evaporation pool, and to the fact that a small part of the flow is discharged from the circulation system to a discharge vessel, in which a lower pressure prevails than in the evaporator. By this discharge of a small part of the flow, a major accumulation of uncondensable gas on the primary side of the evaporator is avoided, which results in a more efficient cooling of the flow in the circulation system upon passage through the evaporator.